1. Field of the Invention
The present invention relates to a dielectric waveguide suitable for a transmission line or. an integrated circuit used in a millimeter wave band or a microwave band.
2. Description of the Related Art
A dielectric waveguide having a dielectric strip between opposing parallel conductors has been used as a transmission line used in a millimeter wave band or a microwave band. In particular, a dielectric waveguide in which the distance between the conductors is set to a value smaller than xc2xd of the wavelength of propagating electromagnetic waves to limit radiated waves at a bent portion of a dielectric strip has been used as a nonradiative dielectric waveguide.
Dielectric waveguides of this kind may be used to form millimeter wave circuit modules and may be connected to each other between the modules. In such a case, dielectric strips are connected to each other. Also, if dielectric strip portions are not integrally formed in a single module, dielectric strips are connected to each other.
FIG. 35 shows a conventional connection between two dielectric strips. Upper and lower electrodes are omitted. Members 1 and 2 are dielectric strips. Dielectric waveguides are connected to each other by opposing the end surfaces of the dielectric strips which are perpendicular to the direction of propagation of electromagnetic energy.
Conventionally, polytetrafluoroethylene (PTFE), which has a small dielectric constant and exhibits a low transmission loss, has been used to make a dielectric strip, and hard aluminum having high workability and having a suitable high hardness has been used as a material for forming an electroconductive plate constituting a dielectric waveguide. However, the difference between the linear expansion coefficients of PTFE and aluminum is so large that a gap is formed between the opposed surfaces of dielectric strips of a dielectric waveguide when the dielectric waveguide is used at a temperature lower than the temperature at the time of assembly. Ordinarily, a certain gap can also exist between the opposed surfaces of dielectric strips according to a working tolerance. Since the dielectric constant of air entering such a gap is different from that of the dielectric strips, reflection of an electromagnetic wave occurs at the gap, resulting in a deterioration in the characteristics of the transmission line. Moreover, at the time of assembly of separate dielectric waveguides, a misalignment may occur between the opposed surfaces of the dielectric strips at the connection between the two dielectric waveguides, which depends upon the assembly accuracy. In such a case, reflection is caused at the connection surfaces, also resulting in a deterioration in the characteristics of the transmission line.
FIG. 36 shows the result of calculation of an S11 (reflection loss) characteristic in a 60 GHz band of a dielectric waveguide which has a sectional configuration such as shown in FIG. 1, and in which, referring to FIG. 1, a=2.2 mm, b=1.8 mm, g=0.5 mm, and in FIG. 35, gap=0.2 mm, LL=10 mm, and the dielectric constant xcex5r of 2.04. The characteristic was calculated by a three-dimensional finite element method. The guide wavelength xcexg at 60 GHz in this case is 8.7 mm. As shown in FIG. 36, even when the gap is small, about 0.2 mm, the reflection loss is xe2x88x9215 dB or larger.
It is an object of the present invention to provide a dielectric waveguide designed to avoid the influence of a gap formed at a connection between dielectric strips and to have an improved characteristic.
According to the present invention, there is provided a dielectric waveguide comprising an electromagnetic wave propagation region formed by disposing a plurality of dielectric strip portions along a direction of propagation of an electromagnetic wave. According to one aspect of the present invention, to avoid the influence of reflection at the connection between each adjacent pair of the dielectric strips, adjacent pairs of the electric strips are connected at a plurality of planes spaced apart from each other in the direction of propagation of an electromagnetic wave by a distance corresponding to an odd number multiple of xc2xc of the guide wavelength of the electromagnetic wave propagating through the dielectric strips.
Thus, the connection planes between the adjacent pairs of the dielectric strips are spaced apart from each other by the distance corresponding to an odd number multiple of xc2xc of the wavelength of an electromagnetic wave in the direction of propagation of the electromagnetic wave to enable electromagnetic waves reflected at the connection planes to be superposed in phase opposition to each other to cancel out, thus reducing the influence of reflection.
According to a second aspect of the present invention, a dielectric strip having a length corresponding to an odd number multiple of xc2xc of the guide wavelength of an electromagnetic wave propagating through two dielectric strips is interposed between the two dielectric strips to connect them to each other.
According to a third aspect of the present invention, a third dielectric strip is inserted in part of a connection section of a first dielectric strip and a second dielectric strip and the strips are connected to each other, and the distances between the three connection planes in said connection section are determined so that a wave reflected at the connection plane between the first and third dielectric strips, a wave reflected at the connection plane between the first and second dielectric strips, and a wave reflected at the connection plane between the second and third dielectric strips are superposed with a phase difference of 2xcfx80/3 from each other. For example, the phase of a reflected wave at the first-third dielectric strip connection plane is 0; the phase of a reflected wave at the first-second dielectric strip connection plane is 2xcfx80/3 (120xc2x0); and the phase of a reflected wave at the second-third dielectric strip connection plane is 4xcfx80/3 (240xc2x0), and if the reflected waves are equal in intensity, each of the real and imaginary part of the resultant wave is zero. Thus, the three reflected waves cancel out.
According to a fourth aspect of the present invention, the distance between the first-second dielectric connection plane and the first-third dielectric strip connection plane is set to ⅙ of the guide wavelength of an electromagnetic wave propagating through the dielectric strips, and the distance between the first-second dielectric strip connection plane and the second-third dielectric strip connection plane is set to ⅙ of the guide wavelength.
According to fifth and sixth aspects of the present invention, to reduce an error in positioning of the opposed surfaces of the dielectric strips at the connection between a pair of dielectric waveguides, the pair of dielectric waveguides are positioned along a direction parallel to the conductor plates and along a direction perpendicular to the electromagnetic wave propagation direction by a projecting portion of one of the conductor plates in the opposed surfaces of the conductor plates at the connection between the pair of dielectric waveguides and a recessed portion of the corresponding opposite conductor plate at a corresponding position.